Soil Retaining Structures

Development of models for structural analysis

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The topic of this thesis is the development of models for the structural analysis of soil retaining structures. The soil retaining structures being looked at are; block revetments, flexible retaining walls and bored tunnels in soft soil. Within this context typical structural behavior of these structures is discussed too. The emphasis within the context of model development is on the use of Finite Element analysis as a generic toolbox for model development. In chapter 3 a methodology for the development of models is formulated. Both verification, the testing of the integrity of a model and the relation with models of lower hierarchy, and evaluation, testing the accuracy of a model are important. Accuracy and uncertainty are related aspects of model development. In chapter 4 an analytical toolbox for the development of models for structural analysis is given. One of the observations in the formulation of this chapter was that groundwater flow can be evaluated based on the same principle as equilibrium of stresses; the principle of virtual work. In the next three chapters 5, 6, and 7 three examples are given of development of models for the structural analysis of soil retaining structures. In chapter 5, a model for the stability against sliding of the top-layer of a revetment is put forward. The model is evaluated against prototype information. The validity to use Delta flume measurements to validate models for the design of a revetments cover-layer is being reconsidered, as there is reason to believe that the undrained response which is attributing to'the strength of a cover-layer has 3 dimensional effects being overlooked in a 2D measurement. In chapter 6, the models for sheet-pile retaining walls are described. The development of finite element analysis for sheet pile walls is described. Subsequently some of the verification analyses are described including an analytical solution derived from plasticity theory. Finally the finite element model is validated against prototype measurements, i.e. the Karlsruhe sheet pile test (1993). Within this context the test is evaluated applying inverse analysis. One of the conclusions was that a distinct difference between the in-situ stiffness of a sand layer and the stiffness as derived from a laboratory test was found. The reason for this is thought to be the breaking up of structure during sampling in advance of the laboratory testing. This structure is not recovered during preparation in the laboratory. The model evaluation indicates that the application of Finite Element analysis improves the accuracy in comparison to the empirical models. In chapter 7, the structural models for the design of a tunnel liner are discussed. The problems related to bored tunnelling in soft soil are discussed. The model hierarchy for the evaluation of the tunnel liner is discussed. In the second part of this chapter, a back-analysis of the measurements from the Second Heinenoord tunnel, with a finite element model is described. From this it comes forward that the uncertainty with respect to tunnel liner design is mainly related to the construction phase, i.e. tunnel ring assembly. In comparison to sheet pile walls, the soil loading of tunnel liners are easier to model.